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It is clear that climate change—or, more appropriately, the climate crisis—is a defining issue of this century. However, it is not yet clear what the solutions to this human-made crisis are. Carbicrete, a company founded by McGill alumni Chris Stern (BEng ‘94) and Mehrdad Mahoutian (Ph.D 2014), is undertaking the ambitious task of redefining one of the most overlooked sources of carbon dioxide emissions: The concrete industry.

Concrete is essentially composed of three basic ingredients: Water; an aggregate, such as gravel, sand, or rock; and cement. The preferred choice of cement in the construction industry today is Portland cement. While cheap and readily available, Portland cement also has a major downside: Its production process is one of the world’s single biggest emitters of carbon dioxide.

To counteract the ongoing climate crisis, scientists agree that carbon dioxide emissions from building materials such as cement must be reduced. But with a material as ubiquitous as concrete, it is impossible to stop using it cold turkey.

In an interview with the The McGill Tribune, Stern, the CEO of Carbicrete, explained how a different manufacturing technique that uses an unexpected byproduct of industrial manufacturing can eliminate the carbon dioxide emissions of concrete production.

“Steel slag, which is a byproduct of the steel-making process, could be used instead of Portland cement to produce a stable carbonate, which is necessary as a binder in concrete,” Stern said.

Using steel slag, Carbicrete is attempting to eliminate Portland cement in manufacturing. The company’s goal is based on Mahoutian’s past research at McGill, which focussed on replacing Portland cement in the concrete production process.

According to Stern, Carbicrete is not only eliminating carbon dioxide emissions but also storing carbon dioxide in their finished product, making Carbicrete’s concrete carbon negative.

“In a regular concrete block, which weighs 18 kilograms, about two kilograms by weight is Portland cement,” Stern said. “By eliminating that cement from the production, which we do by replacing it with steel slag, we eliminate that source of carbon dioxide emissions.”

To produce the binding carbonate, steel slag must react with carbon dioxide, which could be taken from emitters such as fossil fuel power plants. Since Carbicrete is still in its pilot phase, the details on how to implement this carbon-storing strategy on an industrial scale have yet to be finalized. Still, Stern is optimistic about the company’s future.

“We are still trying to figure out how we are going to get large quantities of carbon dioxide to use for production,” Stern said. “One potential scenario is steel plants [….] There’s already the steel slag coming as a byproduct from the manufacturing, and then there is the carbon dioxide from smelting. Add it together, and you’ve got a product [….] It’s like Christmas Day.”

Start-ups like Carbicrete allow freedom to develop innovative products in a work environment different to that of larger companies. For students, Stern stressed the importance of taking a leap of faith and carving your own career path.

“Any student who wants to do something different instead of working for some big company shouldn’t hesitate,” Stern said. “I wouldn’t say working for big companies is a waste, but it isn’t for everyone. Had I known [this] when I graduated from McGill in 1994, I would have done things differently.”

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McGill University is located on land which has long served as a site of meeting and exchange amongst Indigenous peoples, including the Haudenosaunee and Anishinabeg nations. The McGill Tribune honours, recognizes and respects these nations as the traditional stewards of the lands and waters on which we meet today.